rustebra 0.3.2

A hybrid no_std/alloc linear algebra crate for Rust, scaling from embedded targets to dynamic Krylov subspace solvers.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301

use alloc::vec;
use alloc::vec::Vec;

use crate::scalar::Scalar;

use super::{CscMatrix, CsrMatrix};

/// Removes stored entries from `m` whose absolute value does not exceed `tolerance`,
/// returning a new `CsrMatrix<T>` with a reduced sparsity pattern and unchanged shape.
///
/// An entry `v` is **kept** when its absolute value strictly exceeds `tolerance`.
/// Setting `tolerance` to `T::zero()` removes only entries that are exactly `0`.
/// Negative `tolerance` is clamped to `T::zero()`. NaN entries are always kept.
///
/// This is useful after repeated sparse additions or Krylov-solver updates, where
/// accumulated fill-in or exact cancellations leave stored zeros that inflate `nnz`
/// without contributing to the matrix value.
///
/// # Examples
///
/// ```
/// use rustebra::sparse::{CsrMatrix, prune_csr};
///
/// // Row 0: three entries — two negligible, one significant.
/// let m = CsrMatrix::new(
///     1, 3,
///     vec![0, 3],
///     vec![0, 1, 2],
///     vec![1e-15_f64, 2.0, -1e-15],
/// )
/// .unwrap();
///
/// let pruned = prune_csr(m, 1e-10);
/// assert_eq!(pruned.nnz(), 1);
/// assert_eq!(pruned.col_indices(), &[1]);
/// assert_eq!(pruned.values(),      &[2.0]);
/// ```
pub fn prune_csr<T: Scalar + PartialOrd>(m: CsrMatrix<T>, tolerance: T) -> CsrMatrix<T> {
    let (rows, cols, old_row_ptr, old_col, old_val) = m.into_raw_parts();
    let tolerance = if tolerance < T::zero() {
        T::zero()
    } else {
        tolerance
    };
    let neg_tol = T::zero().sub(tolerance);

    let mut new_row_ptr = vec![0usize; rows + 1];
    let mut new_col: Vec<usize> = Vec::new();
    let mut new_val: Vec<T> = Vec::new();

    for r in 0..rows {
        for k in old_row_ptr[r]..old_row_ptr[r + 1] {
            let v = old_val[k];
            if !(v <= tolerance && v >= neg_tol) {
                new_col.push(old_col[k]);
                new_val.push(v);
            }
        }
        new_row_ptr[r + 1] = new_col.len();
    }

    CsrMatrix::new_raw(rows, cols, new_row_ptr, new_col, new_val)
}

/// Removes stored entries from `m` whose absolute value does not exceed `tolerance`,
/// returning a new `CscMatrix<T>` with a reduced sparsity pattern and unchanged shape.
///
/// An entry `v` is **kept** when its absolute value strictly exceeds `tolerance`.
/// Setting `tolerance` to `T::zero()` removes only entries that are exactly `0`.
/// Negative `tolerance` is clamped to `T::zero()`. NaN entries are always kept.
///
/// This is the CSC counterpart to [`prune_csr`], providing symmetric support for both
/// sparse matrix formats.
///
/// # Examples
///
/// ```
/// use rustebra::sparse::{CscMatrix, prune_csc};
///
/// // Column 0: three entries — two negligible, one significant.
/// let m = CscMatrix::new(
///     3, 1,
///     vec![0, 3],
///     vec![0, 1, 2],
///     vec![1e-15_f64, 2.0, -1e-15],
/// )
/// .unwrap();
///
/// let pruned = prune_csc(m, 1e-10);
/// assert_eq!(pruned.nnz(), 1);
/// assert_eq!(pruned.row_indices(), &[1]);
/// assert_eq!(pruned.values(),      &[2.0]);
/// ```
pub fn prune_csc<T: Scalar + PartialOrd>(m: CscMatrix<T>, tolerance: T) -> CscMatrix<T> {
    let (rows, cols, old_col_ptr, old_row, old_val) = m.into_raw_parts();
    let tolerance = if tolerance < T::zero() {
        T::zero()
    } else {
        tolerance
    };
    let neg_tol = T::zero().sub(tolerance);

    let mut new_col_ptr = vec![0usize; cols + 1];
    let mut new_row: Vec<usize> = Vec::new();
    let mut new_val: Vec<T> = Vec::new();

    for c in 0..cols {
        for k in old_col_ptr[c]..old_col_ptr[c + 1] {
            let v = old_val[k];
            if !(v <= tolerance && v >= neg_tol) {
                new_row.push(old_row[k]);
                new_val.push(v);
            }
        }
        new_col_ptr[c + 1] = new_row.len();
    }

    CscMatrix::new_raw(rows, cols, new_col_ptr, new_row, new_val)
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::sparse::CsrMatrix;

    #[test]
    fn keeps_entries_outside_tolerance_band() {
        let m = CsrMatrix::new(
            1,
            3,
            vec![0, 3],
            vec![0, 1, 2],
            vec![1e-15_f64, 2.0, -1e-15],
        )
        .unwrap();
        let p = prune_csr(m, 1e-10);
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.col_indices(), &[1]);
        assert_eq!(p.values(), &[2.0]);
    }

    #[test]
    fn zero_tolerance_removes_exact_zeros() {
        let m = CsrMatrix::new(1, 3, vec![0, 3], vec![0, 1, 2], vec![0.0_f64, 5.0, 0.0]).unwrap();
        let p = prune_csr(m, 0.0);
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.col_indices(), &[1]);
    }

    #[test]
    fn keeps_negative_values_outside_band() {
        let m = CsrMatrix::new(1, 2, vec![0, 2], vec![0, 1], vec![-3.0_f64, 0.5]).unwrap();
        let p = prune_csr(m, 1.0);
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.col_indices(), &[0]);
        assert_eq!(p.values(), &[-3.0]);
    }

    #[test]
    fn preserves_row_structure_with_multi_row_matrix() {
        // Row 0 keeps one entry; row 1 is fully pruned; row 2 keeps both.
        let m = CsrMatrix::new(
            3,
            3,
            vec![0, 2, 4, 6],
            vec![0, 1, 0, 1, 0, 1],
            vec![1e-15_f64, 5.0, 1e-14, 1e-13, 7.0, 8.0],
        )
        .unwrap();
        let p = prune_csr(m, 1e-10);
        assert_eq!(p.row_ptr(), &[0, 1, 1, 3]);
        assert_eq!(p.col_indices(), &[1, 0, 1]);
        assert_eq!(p.values(), &[5.0, 7.0, 8.0]);
    }

    #[test]
    fn all_entries_below_tolerance_gives_empty_matrix() {
        let m = CsrMatrix::new(2, 2, vec![0, 1, 2], vec![0, 1], vec![1e-20_f64, 1e-20]).unwrap();
        let p = prune_csr(m, 1e-10);
        assert_eq!(p.nnz(), 0);
        assert_eq!(p.row_ptr(), &[0, 0, 0]);
    }

    #[test]
    fn empty_matrix_unchanged() {
        let m = CsrMatrix::<f64>::new(3, 3, vec![0, 0, 0, 0], vec![], vec![]).unwrap();
        let p = prune_csr(m, 1e-10);
        assert_eq!(p.nnz(), 0);
        assert_eq!(p.rows(), 3);
    }

    #[test]
    fn negative_tolerance_clamped_to_zero() {
        // Negative tolerance must not invert the predicate and keep everything.
        let m = CsrMatrix::new(1, 3, vec![0, 3], vec![0, 1, 2], vec![0.0_f64, 5.0, 0.0]).unwrap();
        let p = prune_csr(m, -1.0);
        // Clamped to 0.0: only exact zeros removed, 5.0 kept.
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.col_indices(), &[1]);
        assert_eq!(p.values(), &[5.0]);
    }

    #[test]
    fn nan_entry_is_kept_not_silently_dropped() {
        let m = CsrMatrix::new(1, 2, vec![0, 2], vec![0, 1], vec![f64::NAN, 2.0]).unwrap();
        let p = prune_csr(m, 1e-10);
        assert_eq!(p.nnz(), 2);
        assert!(p.values()[0].is_nan());
        assert_eq!(p.values()[1], 2.0);
    }
}

#[cfg(test)]
mod tests_csc {
    use super::*;
    use crate::sparse::CscMatrix;

    #[test]
    fn csc_keeps_entries_outside_tolerance_band() {
        let m = CscMatrix::new(
            3,
            1,
            vec![0, 3],
            vec![0, 1, 2],
            vec![1e-15_f64, 2.0, -1e-15],
        )
        .unwrap();
        let p = prune_csc(m, 1e-10);
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.row_indices(), &[1]);
        assert_eq!(p.values(), &[2.0]);
    }

    #[test]
    fn csc_zero_tolerance_removes_exact_zeros() {
        let m = CscMatrix::new(3, 1, vec![0, 3], vec![0, 1, 2], vec![0.0_f64, 5.0, 0.0]).unwrap();
        let p = prune_csc(m, 0.0);
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.row_indices(), &[1]);
    }

    #[test]
    fn csc_keeps_negative_values_outside_band() {
        let m = CscMatrix::new(2, 1, vec![0, 2], vec![0, 1], vec![-3.0_f64, 0.5]).unwrap();
        let p = prune_csc(m, 1.0);
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.row_indices(), &[0]);
        assert_eq!(p.values(), &[-3.0]);
    }

    #[test]
    fn csc_preserves_column_structure_with_multi_column_matrix() {
        // Column 0 keeps one entry; column 1 is fully pruned; column 2 keeps both.
        let m = CscMatrix::new(
            3,
            3,
            vec![0, 2, 4, 6],
            vec![0, 1, 0, 1, 0, 1],
            vec![1e-15_f64, 5.0, 1e-14, 1e-13, 7.0, 8.0],
        )
        .unwrap();
        let p = prune_csc(m, 1e-10);
        assert_eq!(p.col_ptr(), &[0, 1, 1, 3]);
        assert_eq!(p.row_indices(), &[1, 0, 1]);
        assert_eq!(p.values(), &[5.0, 7.0, 8.0]);
    }

    #[test]
    fn csc_all_entries_below_tolerance_gives_empty_matrix() {
        let m = CscMatrix::new(2, 2, vec![0, 1, 2], vec![0, 1], vec![1e-20_f64, 1e-20]).unwrap();
        let p = prune_csc(m, 1e-10);
        assert_eq!(p.nnz(), 0);
        assert_eq!(p.col_ptr(), &[0, 0, 0]);
    }

    #[test]
    fn csc_empty_matrix_unchanged() {
        let m = CscMatrix::<f64>::new(3, 3, vec![0, 0, 0, 0], vec![], vec![]).unwrap();
        let p = prune_csc(m, 1e-10);
        assert_eq!(p.nnz(), 0);
        assert_eq!(p.cols(), 3);
    }

    #[test]
    fn csc_negative_tolerance_clamped_to_zero() {
        let m = CscMatrix::new(3, 1, vec![0, 3], vec![0, 1, 2], vec![0.0_f64, 5.0, 0.0]).unwrap();
        let p = prune_csc(m, -1.0);
        assert_eq!(p.nnz(), 1);
        assert_eq!(p.row_indices(), &[1]);
        assert_eq!(p.values(), &[5.0]);
    }

    #[test]
    fn csc_nan_entry_is_kept_not_silently_dropped() {
        let m = CscMatrix::new(2, 1, vec![0, 2], vec![0, 1], vec![f64::NAN, 2.0]).unwrap();
        let p = prune_csc(m, 1e-10);
        assert_eq!(p.nnz(), 2);
        assert!(p.values()[0].is_nan());
        assert_eq!(p.values()[1], 2.0);
    }
}